Fuel cell power systems have been proposed as a clean, efficient and environmentally responsible power source for electric vehicles and various other applications. One type of fuel cell power system employs use of a proton exchange membrane (PEM) to catalytically facilitate reaction of fuels (such as hydrogen) and oxidants (such as air or oxygen) into electricity. Typically, the fuel cell power system has more than one fuel cell that includes an anode and a cathode with the PEM therebetween. The anode receives the hydrogen gas and the cathode receives the oxygen. The hydrogen gas is ionized in the anode to generate free hydrogen ions and electrons. The hydrogen ions pass through the electrolyte to the cathode. The hydrogen ions react with the oxygen and the electrons in the cathode to generate water as a by-product. The electrons from the anode cannot pass through the PEM, and are instead directed through a load to perform work before being sent to the cathode. The work acts to operate the vehicle. Many fuels cells are combined in a fuel cell stack to generate the desired power.
The fuel cell power system can include a processor that converts a liquid fuel, such as alcohols (e.g., methanol or ethanol), hydrocarbons (e.g., gasoline), and/or mixtures thereof, such as blends of ethanol/methanol and gasoline, to the hydrogen gas for the fuel cell stack. Such liquid fuels are easy to store on the vehicle. Further, there is a nationwide infrastructure for supplying the liquid fuels. Gaseous hydrocarbons, such as methane, propane, natural gas, LPG, etc., are also suitable fuels for both vehicle and non-vehicle fuel cell applications. Various reformers or processors are known in the art for converting the liquid fuel to gaseous hydrogen suitable for the fuel cell.
Alternatively, the hydrogen gas can be processed separate from the vehicle and stored at a filling station and the like. The hydrogen gas is transferred from the filling station to a high pressure vessel or container on the vehicle to supply the desired hydrogen gas to the fuel cell engine as needed. The high pressure vessels are typically classified into one of four types: a Type I vessel having an all-metal construction; a Type II having a metal-lined construction with a fiber hoop wrap for reinforcement; a Type III having a metal-lined construction with a complete fiber reinforcement wrap; and a Type IV having a plastic-lined construction with a complete fiber reinforcement wrap.
Tensile strains on the winding reinforcement wrap of the Type II, Type III, and Type IV high pressure vessel are caused by a pressure of a fluid contained within the pressure vessel. However, the reinforcement wrap is typically not loaded to a maximum tensile strength across the thickness of the wrap due to a phenomenon known as the “thick wall effect.” For reinforcement wraps of conventional wall thickness, the thick wall effect states that a strain gradient is observed through the thickness of the wall. The strain gradient is typically characterized by a strain at an outer layer being lower than a strain at an inner layer.
It has been shown that an initial rupture at the inner layer of the fiber reinforcement wrap results in the outer layers of the reinforcement wrap becoming overloaded. The remaining load capacity provided by the outer layers normally cannot compensate for a rupture in the inner layers. Thus, the strength of the composite wrap is limited by the strength of the inner layers, and the remaining reinforcement wrap is not fully utilized in known pressure vessels.
U.S. Pat. No. 4,438,858 to Grover, incorporated herein by referenced in its entirety, states that an important parameter in controlling the strain gradient is a transverse or radial stiffness of the composite material. The transverse stiffness is influenced by a wind angle of the vessel, as well as any delamination or other defects induced during fabrication.
Also disclosed in U.S. Pat. No. 6,651,307 to Portmann, incorporated herein by reference in its entirety, is a fiber-reinforced pressure vessel having a composite layer applied over a liner to increase the strength of the vessel. The fibers wrapped about the liner act in tension when the vessel is pressurized. It is known according to Portmann to pre-stress the liner and fiber wrap to increase the vessel's structural characteristics under pressure.
There is a continuing need for a high pressure vessel having a more even distribution of stress across a thickness of a fiber reinforcement wrap. Desirably, the utilization of the fiber reinforcement wrap is optimized and the employment of material is minimized, thereby minimizing a weight of the pressure vessel.